The chassis length also changes with the height so a rough correlationbetween the two is

33" = 76"35" = 80"37" = 82"39" = 84"

To find out the fit of a car have your child wearing their helmet sit on the floor with their back against the wall and measure to the top of their helmet and add one inch. That is the minimum height you need for QMA rules, must have at least one inch of head room clearance from the roll bars.

As a rule of thumb, you would like the overhaul size of your car to be proportionate to the size of your driver.